Spin fluctuations, magnetic long-range order and Fermi surface gapping in NaxCoO2 (2008)
Schulze, T. F., Bruehwiler, M., Haefliger, P. S., Kazakov, S. M., Niedermayer, Ch., Mattenberger, K., ...
In this study an extended low energy phase diagram for NaxCoO2 is experimentally established with emphasis on the high x range. It is based on systematic heat capacity studies on both polycrystalline...
Akrap, A., Tutis, E., Kazakov, S. M., Zhigadlo, N. D., Karpinski, J., Forro, L.
We performed high-pressure transport measurements on high-quality single crystals of KOs2O6, a beta-pyrochlore superconductor. While the resistivity at high temperatures might approach saturation,...
Dubois, C., Santi, G., Cuttat, I., Berthod, C., Jenkins, N., Petrović, A. P., ...
We performed the first scanning tunneling spectroscopy measurements on the pyrochlore superconductor KOs2O6 (Tc = 9.6 K) in both zero magnetic field and the vortex state at several temperatures above...
Coexistence of superconductivity and incoherence in quasi 1D chains (2006)
Khasanov, R., Kondo, T., Schmalian, J., Kazakov, S. M., Zhigadlo, N. D., Karpinski, J., ...
The dimensionality of a correlated many-body system has a large impact on its electronic properties. When electrons are confined to one-dimensional chains of atoms their behavior is very different...
Kondo, T., Khasanov, R., Karpinski, J., Kazakov, S. M., Zhigadlo, N. D., Ohta, T., ...
We use microprobe Angle-Resolved Photoemission Spectroscopy (muARPES) to separately investigate the electronic properties of CuO2 planes and CuO chains in the high temperature superconductor,...
Quenching of the Haldane gap in LiVSi2O6 and related compounds (2006)
Pedrini, B., Wessel, S., Gavilano, J. L., Ott, H. R., Kazakov, S. M., Karpinski, J.
We report results of susceptibility chi and 7Li NMR measurements on LiVSi2O6. The temperature dependence of the magnetic susceptibility chi(T) exhibits a broad maximum, typical for low-dimensional...
Brühwiler, M., Kazakov, S. M., Karpinski, J., Batlogg, B.
To assess electron correlation and electron-phonon coupling in the recently discovered beta-pyrochlores KOs2O6 and RbOs2O6, we have performed specific heat measurements in magnetic fields up to 14 T....
Phonon dispersion and lifetimes in MgB2 (2006)
Shukla, Abhay, Calandra, Matteo, D'Astuto, Matteo, Lazzeri, Michele, Mauri, Francesco, Bellin, Christophe, ...
We measure phonon dispersion and linewidth in a single crystal of MgB_2 along the Gamma-A, Gamma-M and A-L directions using inelastic X-Ray scattering. We use Density Functional Theory to compute the...
NaxCoO2: Enhanced low-energy excitations of electrons on a 2D triangular lattice (2006)
Brühwiler, M., Batlogg, B., Kazakov, S. M., Niedermayer, Ch., Karpinski, J.
To elucidate the low-energy excitation spectrum of correlated electrons on a 2D triangular lattice, we have studied the electrical resistance and specific heat down to 0.5 K and in magnetic fields up...
Large mass enhancement in RbOs2O6 (2006)
Brühwiler, M., Kazakov, S. M., Karpinski, J., Batlogg, B.
Heat capacity measurements on the recently discovered geometrically frustrated beta-pyrochlore superconductor RbOs2O6 (Tc=6.4 K) yield a Sommerfeld coefficient of 44 mJ/(molf.u. K^2). This is about 4...
Crystal growth, structural studies and superconducting properties of beta-pyrochlore KOs2O6 (2006)
Schuck, G., Kazakov, S. M., Rogacki, K., Zhigadlo, N. D., Karpinski, J.
Single crystals of KOs2O6 have been grown in a sealed quartz ampoule. Detailed single crystal X-ray diffraction studies at room temperature show Bragg peaks that violate Fd-3m symmetry. With a...
Recent progres in Vortex Studies by Tunneling Spectroscopy (2006)
Kohen, A., Cren, T., Noat, Y., Proslier, Th., Giubileo, F., Bobba, F., ...
Among the methods used to study the vortex state in superconductors, scanning tunneling spectroscopy (STS), is unique in its ability to measure in real space the variations in the local quasiparticle...
"Lazy Fisherman" Method of Vortex Analysis: Application to MgB2 (2006)
Kohen, A., Giubileo, F., Bobba, F., Proslier, Th., Zhigadlo, N., Kazakov, S.M., ...
Among the different methods of vortex study in superconductors, Scanning Tunneling Microscopy (STM) and Spectroscopy (STS), occupies a particular place. Due to its extraordinary spatial and energy...
Localized versus itinerant magnetic moments in Na0.72CoO2 (2005)
Gavilano, J. L., Pedrini, B., Magishi, K., Hinderer, J., Weller, M., Ott, H. R., ...
Based on experimental 59Co-NMR data in the temperature range between 0.1 and 300 K, we address the problem of the character of the Co 3d-electron based magnetism in Na0.7CoO2. Temperature dependent...
Strong magnetic pair breaking in Mn substituted MgB_2 single crystals (2005)
Rogacki, K., Batlogg, B., Karpinski, J., Zhigadlo, N. D., Schuck, G., Kazakov, S. M., ...
Magnetic ions (Mn) were substituted in MgB_2 single crystals resulting in a strong pair-breaking effect. The superconducting transition temperature, T_c, in Mg_{1-x}Mn_xB_2 has been found to be...
Guritanu, V., Kuzmenko, A. B., Kazakov, S. M., Zhigadlo, N. D., Karpinski, J.
We present the anisotropic optical conductivity of MgB$_{2}$ between 0.1 and 3.7 eV at room temperature obtained on single crystals of different purity by the spectroscopic ellipsometry and...
Magnetic Phase Transition at 88 K in Na0.5CoO2 revealed by 23Na-NMR investigations (2005)
Pedrini, B., Gavilano, J. L., Weyeneth, S., Felder, E., Hinderer, J., Weller, M., ...
Na0.5CoO2 exhibits a metal-insulator transition at 53 K upon cooling. The nature of another transition at 88 K has not been fully clarified yet. We report the results of measurements of the...
Kohen, A., Cren, T., Proslier, Th., Noat, Y., Giubileo, F., Bobba, F., ...
We introduce a mode of operation for studying the vortex phase in superconductors using scanning tunnelling microscopy (STM). While in the conventional STM method, the tip is scanned over a sample in...
de Haas-van Alphen effect investigation of the electronic structure of Al substituted MgB_2 (2005)
Carrington, A., Fletcher, J. D., Cooper, J. R., Taylor, O. J., Balicas, L., Zhigadlo, N. D., ...
We report a de Haas-van Alphen (dHvA) study of the electronic structure of Al doped crystals of MgB$_2$. We have measured crystals with $\sim 7.5$% Al which have a $T_c$ of 33.6 K, ($\sim 14$% lower...
Schneider, T., Khasanov, R., Karpinski, J., Kazakov, S. M., Keller, H.
The effect of the magnetic field on the critical behavior of RbOs2O6 is investigated. We present and analyze magnetization data, revealing remarkable consistency with a magnetic field induced finye...
Brühwiler, M., Kazakov, S. M., Karpinski, J., Batlogg, B.
We develop a general procedure for the analysis of bulk thermodynamic data of a superconductor for samples containing a metallic non-superconducting second phase. The method is based on the...
Temperature dependent anisotropy of the penetration depth and coherence length in MgB$_2 (2005)
Fletcher, J. D., Carrington, A., Taylor, O. J., Kazakov, S. M., Karpinski, J.
We report measurements of the temperature dependent anisotropies ($\gamma_\lambda$ and $\gamma_\xi$) of both the London penetration depth $\lambda$ and the upper critical field of MgB$_2$. Data for...
Anomaly in YBa2Cu4O8 charge distribution below Tc: A zero-field muon spin relaxation study (2005)
Carretta, P, Keren, A, Lord, J S, Zucca, I, Kazakov, S M, Karpinski, J
Zero-field muon spin-relaxation (µSR) measurements in 63Cu isotope enriched and natural YBa2Cu4O8 powders are presented. The µ+ relaxation rate is characterized by a sizeable enhancement as the...
Study of pressure effect on the magnetic penetration depth in MgB$_2$ (2004)
Di Castro, D., Khasanov, R., Grimaldi, C., Karpinski, J., Kazakov, S. M., Keller, H.
A study of the pressure effect on the magnetic penetration depth $\lambda$ in polycrystalline MgB$_{2}$ was performed by measuring the temperature dependence of the magnetization under an applied...
Study of the magnetic penetration depth in RbOs_2O_6 (2004)
Khasanov, R., Eshchenko, D. G., Di Castro, D., Shengelaya, A., La Mattina, F., Maisuradze, A., ...
Measurements of the magnetic field penetration depth \lambda in the pyrochlore superconductor RbOs_2O_6 (T_c\simeq6.3 K) were carried out by means of the muon-spin-rotation (\muSR) technique. At low...
Al substitution in MgB2 crystals: influence on superconducting and structural properties (2004)
Karpinski, J., Zhigadlo, N. D., Schuck, G., Kazakov, S. M., Batlogg, B., Rogacki, K., ...
Single crystals of Mg1-xAlxB2 have been grown at a pressure of 30 kbar using the cubic anvil technique. Precipitation free crystals with x < 0.1 were obtained as a result of optimization of already...
Evidence for s-wave superconductivity in the new beta-pyrochlore oxide RbOs2O6 (2004)
Magishi, K., Gavilano, J. L., Pedrini, B., Hinderer, J., Weller, M., Ott, H. R., ...
We report the results of 87Rb NMR measurements on RbOs2O6, a new member of the family of the superconducting pyrochlore-type oxides with a critical temperature Tc = 6.4 K. In the normal state, the...
Influence of carbon substitution on the heat transport in single crystalline MgB2 (2004)
Sologubenko, A. V., Zhigadlo, N. D., Kazakov, S. M., Karpinski, J., Ott, H. R.
We report data on the thermal conductivity \kappa(T,H) in the basal plane of hexagonal single-crystalline and superconducting Mg(B_{1-x}C_x)_2 (x= 0.03, 0.06) at temperatures between 0.5 and 50 K,...
Anomaly in YBa2Cu4O8 charge distribution below Tc: a zero-field muSR study (2004)
Carretta, P., Keren, A., Lord, J. S., Zucca, I., Kazakov, S. M., Karpinski, J.
Zero-field $\mu$SR measurements in $^{63}$Cu isotope enriched and natural YBa$_2$Cu$_4$O$_8$ powders are presented. The temperature dependence of the $\mu^+$ relaxation rate is characterized by a...
Gonnelli, R. S., Daghero, D., Calzolari, A., Ummarino, G. A., Dellarocca, Valeria, Stepanov, V. A., ...
We report the results of the first directional point-contact measurements in Mg(B_{1-x}C_{x})_2 single crystals with 0.047
Gonnelli, R. S., Daghero, D., Ummarino, G. A., Calzolari, A., Dellarocca, Valeria, Stepanov, V. A., ...
We present the results of directional point-contact spectroscopy in state-of-the-art Mg_{1-x}Al_xB_2 and Mg(B_{1-y}C_{y})_2 single crystals produced at ETH, Zurich. Fitting the conductance curves of...
Anisotropy and internal field distribution of MgB2 in the mixed state at low temperatures (2004)
Angst, M., Di Castro, D., Eshchenko, D. G., Khasanov, R., Kohout, S., Savic, I. M., ...
Magnetization and muon spin relaxation on MgB2 were measured as a function of field at 2 K. Both indicate an inverse-squared penetration depth strongly decreasing with increasing field H below about...
Damping of the de Haas-van Alphen oscillations in the superconducting state of MgB_2 (2004)
Fletcher, J. D., Carrington, A., Kazakov, S. M., Karpinski, J.
The de Haas-van Alphen (dHvA) signal arising from orbits on the $\pi$ Fermi surface sheet of the two-gap superconductor MgB$_2$ has been observed in the vortex state below $H_{c2}$. An extra...
Carbon substitution in MgB2 single crystals: structural and superconducting properties (2004)
Kazakov, S. M., Puzniak, R., Rogacki, K., Mironov, A. V., Zhigadlo, N. D., Jun, J., ...
Growth of carbon substituted magnesium diboride Mg(B1-xCx)2 single crystals with 0
Puzniak, R., Angst, M., Szewczyk, A., Jun, J., Kazakov, S. M., Karpinski, J.
The upper critical field Hc2||c(0) of 85 kOe in Mg(B0.94C0.06)2 single crystals, determined from torque measurements, is more than twice as large as that one of 31 kOe in unsubstituted MgB2....
Khasanov, R., Eshchenko, D. G., Karpinski, J., Kazakov, S. M., Zhigadlo, N. D., Brütsch, R., ...
We report magnetization measurements under high hydrostatic pressure in the newly discovered pyrochlore superconductor RbOs_2O_6 (T_c\simeq6.3K at p=0). A pronounced and {\it positive} pressure...
Two regimes in the magnetic field response of superconducting MgB$_2$ (2004)
Kohen, A., Giubileo, F., Proslier, Th., Bobba, F., Noat, Y., Troianovski, A., ...
Using Scanning Tunneling Microscope at low temperature we explore the superconducting phase diagram in the $\pi$-band of the two-band superconductor MgB$_2$. In this band the peculiar shape of the...
Synthesis of superconducting pyrochlore RbOs2O6 (2004)
Kazakov, S. M., Zhigadlo, N. D., Brühwiler, M., Batlogg, B., Karpinski, J.
RbOs2O6, the third superconducting pyrochlore oxide (known so far), has been synthesized by encapsulation and by high pressure techniques. Suitable post chemical treatment of the as-prepared sample...
Superconductivity in Geometrically Frustrated Pyrochlore RbOs2O6 (2004)
Brühwiler, M., Kazakov, S. M., Zhigadlo, N. D., Karpinski, J., Batlogg, B.
We report the basic thermodynamic properties of the new geometrically frustrated beta-pyrochlore bulk superconductor RbOs2O6 with a critical temperature Tc = 6.4 K. Specific heat measurements are...
NMR and dc-susceptibility studies of NaVGe2O6 (2004)
Pedrini, B., Gavilano, J. L., Rau, D., Ott, H. R., Kazakov, S. M., Karpinski, J., ...
We report the results of measurements of the dc magnetic susceptibility chi(T) and of the 23Na nuclear magnetic resonance (NMR) response of NaVGe2O6, a material in which the V ions form a network of...
Point-Contact Spectroscopy in MgB_2: from Fundamental Physics to Thin-Film Characterization (2003)
Gonnelli, R. S., Daghero, D., Calzolari, A., Ummarino, G. A., Dellarocca, V., Stepanov, V. A., ...
In this paper we highlight the advantages of using point-contact spectroscopy (PCS) in multigap superconductors like MgB_2, both as a fundamental research tool and as a non-destructive diagnostic...
Evidence for two electronic components in NaxCoO2 (x = 0.7-0.75) (2003)
Brühwiler, M., Batlogg, B., Kazakov, S. M., Karpinski, J.
Thermodynamic and transport measurements on NaxCoO2 (x ~ 0.7-0.75) over a wide temperature range reveal a strongly enhanced low energy excitation spectrum. The zero-field specific heat and resistance...
Unconventional Charge Ordering in Na0.70CoO2 below 300 K (2003)
Gavilano, J. L., Rau, D., Pedrini, B., Hinderer, J., Ott, H. R., Kazakov, S. M., ...
We present the results of measurements of the dc-magnetic susceptibility chi(T) and the 23Na-NMR response of Na_{0.70}CoO_{2} at temperatures between 50 and 340 K. The chi(T) data suggest that for T...
Gonnelli, R. S., Daghero, D., Calzolari, A., Ummarino, G. A., Dellarocca, Valeria, Stepanov, V. A., ...
We present the results of directional point-contact measurements in MgB_2 single crystals, in magnetic fields up to 9 T parallel to the c axis. By fitting the conductance curves of our point contacts...
Diffusive energy transport in the S=1 Haldane chain compound AgVP2S6 (2003)
Sologubenko, A. V., Kazakov, S. M., Ott, H. R., Asano, T., Ajiro, Y.
We present the results of measurements of the thermal conductivity $\kappa$ of the spin S=1 chain compound AgVP_2S_6 in the temperature range between 2 and 300 K and with the heat flow directed...
Absence of a boron isotope effect in the magnetic penetration depth of MgB$_{2}$ (2003)
Di Castro, D., Angst, M., Eshchenko, D. G., Khasanov, R., Roos, J., Savić, I. M., ...
The magnetic penetration depth $\lambda(0)$ in polycrystalline MgB$_{2}$ for different boron isotopes ($^{10}$B/$^{11}$B) was investigated by transverse field muon spin rotation. No boron isotope...
Gonnelli, R S, Daghero, D, Ummarino, G A, Della Rocca, V, Calzolari, A, Stepanov, V A, ...
The results of the first directional point-contact measurements in MgB2 single crystals, in the presence of magnetic fields up to 9 T either parallel or perpendicular to the ab planes, are presented....
Gonnelli, R. S., Daghero, D., Ummarino, G. A., Dellarocca, Valeria, Calzolari, A., Stepanov, V. A., ...
The results of the first directional point-contact measurements in MgB2 single crystals, in the presence of magnetic fields up to 9 T either parallel or perpendicular to the ab planes, are presented....
Perkins, G. K., Bugoslavsky, Y., Caplin, A . D., Moore, J., Tate, T. J., Gwilliam, R., ...
We present magnetisation data on crystalline and polycrystalline MgB2 before and after irradiation with ~1MeV protons. In the virgin crystal the critical current density is below our noise floor of...
Single crystal growth and properties of MgB2 and Mg(B1-xCx)2 (2003)
Kazakov, S. M., Karpinski, J., Jun, J., Geiser, P., Zhigadlo, N. D., Puzniak, R., ...
Single crystals of MgB2 and Mg(B1-xCx)2 have been grown using cubic anvil technique. Tc values vary in a wide range (39-9 K) with carbon content varying from 0 up to 16%. Using SiC as the precursor...
MgB2 and Mg1-xAlxB2 single crystals: high-pressure growth and physical properties (2003)
Karpinski, J., Kazakov, S. M., Jun, J., Zhigadlo, N. D., Angst, M., Puzniak, R., ...
Single crystals of MgB2 have been grown with a high-pressure cubic anvil technique. They grow via the peritectic decomposition of the MgNB9 ternary nitride. The crystals are of a size up to...
Determination of the Fermi Surface of MgB$_2$ by the de Haas-van Alphen effect (2003)
Carrington, A., Meeson, P. J., Cooper, J. R., Balicas, L., Hussey, N. E., Yelland, E. A., ...
We report measurements of the de Haas-van Alphen effect for single crystals of MgB$_2$, in magnetic fields up to 32 Tesla. In contrast to our earlier work, dHvA orbits from all four sheets of the...
Anisotropic properties of MgB2 by torque magnetometry (2003)
Angst, M., Di Castro, D., Puzniak, R., Wisniewski, A., Jun, J., Kazakov, S. M., ...
Anisotropic properties of superconducting MgB2 obtained by torque magnetometry are compared to theoretical predictions, concentrating on two issues. Firstly, the angular dependence of Hc2 is shown to...
Single crystal growth of MgB2 and thermodynamics of Mg-B-N system at high pressure (2003)
Karpinski, J., Kazakov, S. M., Jun, J., Angst, M., Puzniak, R., Wisniewski, A., ...
Single crystals of MgB2 have been grown at high pressure via the peritectic decomposition of MgNB9. The crystals are of a size up to 1.5x0.9x0.2 mm3 with a weight up to 0.23 mg, and typically have...
Phonon dispersion and lifetimes in MgB2 (2003)
Shukla, Abhay, Calandra, Matteo, D'Astuto, Matteo, Lazzeri, Michele, Mauri, Francesco, Bellin, Christophe, ...
We measure phonon dispersion and linewidth in a single crystal of MgB_2 along the Gamma-A, Gamma-M and A-L directions using inelastic X-Ray scattering. We use Density Functional Theory to compute the...
Phonon dispersion and lifetimes in MgB2 (2003)
Shukla, Abhay, Calandra, Matteo, D'Astuto, Matteo, Lazzeri, Michele, Mauri, Francesco, Bellin, Christophe, ...
We measure phonon dispersion and linewidth in a single crystal of MgB_2 along the Gamma-A, Gamma-M and A-L directions using inelastic X-Ray scattering. We use Density Functional Theory to compute the...
Angst, M., Puzniak, R., Wisniewski, A., Roos, J., Keller, H., Miranovic, P., ...
The angular and temperature dependence of the upper critical field Hc2 in MgB2 was determined from torque magnetometry measurements on single crystals. The Hc2 anisotropy gamma_H was found to...
Point-contact spectroscopy in MgB2 single crystals in magnetic field (2002)
Daghero, D., Gonnelli, R. S., Ummarino, G. A., Stepanov, V. A., Jun, J., Kazakov, S. M., ...
We present the results of a spectroscopic study of state-of-the-art MgB2 single crystals, carried out by using a modified point-contact technique. The use of single crystals allowed us to obtain...